Cast engine blocks can be classified into two basic styles, closed or open deck constructions, the deck being the block surface upon which is mounted the engine head for closing the combustion chambers of the engine. A closed deck is one where the interior chambers of the block, such as water passages, do not interrupt the deck surface except for small transfer or circulation ports. An open deck is one where the die forming members for the cylinder walls and water jacket must penetrate the plane of the deck to shape the interior spaces of the cast object. The need for allowing the dies to enter and be withdrawn through the deck surface prohibits the use of undercut surfaces and, of course, dictates that the area of the deck through which the dies pass must remain open.
Most engine blocks heretofore have been made as closed deck designs, the blocks being cast in sand molds by gravity pouring methods using molten grey iron as the castable material. The benefits of a closed deck design include: (a) greater stability against thermal deformation during engine use, and (b) more accurate wall definition during casting. Internal chambers for a water jacket adjacent the engine cylinders are usually defined by totally enclosed sand cores bonded by chemically cured or heat cured resins. The sand grains are removed from the closed type of casting structure by use of vibration or impact forces which disintegrate the sand core (which has become more brittle by the heat of casting). Such closed deck designs have worked well because (a) the use of iron as the castable material makes the sand cores brittle and thereby easy to remove, and (b) the use of little or no pressure on the casting medium and thus little or no pressure on the cores employed.
With the advent of lighter engine blocks and the need for higher productivity, engine designers are turning to high pressure die casting for the casting of aluminum blocks. Such blocks have been made as open deck designs because of the inherent requirement for withdrawal of the permanent dies from the casting cavity. One of the concerns of the present invention is to provide the benefits of a closed deck engine block design, but fabricated by the use of high pressure die casting techniques.